From Computational Aesthetics 2009

A WikiAdministrator can make a lot of customizations simply by setting variables in the local/config.php file. Any group or page can also have its own configuration file.

From its inception, PmWiki has been designed so that WikiAdministrators can greatly customize the way PmWiki displays pages and the markup sequences used to generate pages. (This is even mentioned explicitly in PmWikiPhilosophy #4.) As a result, the core pmwiki.php script makes extensive use of PmWiki.Variables to determine how markup sequences will be processed and what each individual page will output.

The bulk of this page describes how customizations work in general, see PmWiki.DocumentationIndex for specific customizations that are commonly performed at many PmWiki installations, including:

The simplest type of customization is merely setting a variable to 1 (or TRUE). Here's an example that enables ?action=diag and ?action=phpinfo actions:

$EnableDiag = 1;

You can begin a line with a "#" (an octothorpe, a.k.a. a hash symbol or pound sign) to add a comment. Additionally, some built-in PmWiki variables take values other than 1 or 0 (true or false). Here's another example that customizes the wiki's behavior with respect to search engine web robots (see Cookbook:ControllingWebRobots):

# Allow the site to be indexed by search engines.
$MetaRobots = 'index,follow';
$EnableRobotCloakActions = 1;

The scripts/ subdirectory (below the directory holding the pmwiki.php script) has many customizations.
The PmWikiCookbook contains many example customizations (recipes) that you can download into the cookbook/ subdirectory,
The first few lines of each of these scripts generally contain instructions about how to enable (and use) the feature provided by the script.

These customizations are included in your config.php site configuration. For most scripts this is done by simply adding lines like:

include_once("cookbook/recipefile.php");

and

include_once("scripts/scriptfile.php");

at the end of the config.php file to enable them.

Some of the scripts are automatically enabled for you via the scripts/stdconfig.php script unless you disable it by setting $EnableStdConfig=0; in local/config.php.

Note that you should strongly resist the temptation to directly modify the pmwiki.php script or the files in the scripts/ subdirectory. Any modifications you make to these files will probably be overwritten whenever you perform a PmWiki.Upgrade. Instead, look at some of the sample scripts for examples of customizations that can be performed from config.php. You can even create your own script to do a customization and use include_once(...) to include it from config.php. If you do make your own customization script, you can safely put it in the cookbook/ subdirectory--it won't get overwritten by an upgrade there. You might also want to submit your customization to the pmwiki-users mailing list or the Cookbook so that others can benefit from your effort and so that it can perhaps be included in future releases of PmWiki.